1. Field of the Invention
The present invention relates to instruments and methods for the non-invasive quantitative measurement of blood analytes. More specifically, this invention relates to a new and improved method of increasing an accuracy characteristic for a quantitative measurement instrument, allowing the quantitative measurement instrument to have a less precise detection capability.
2. Description of Background Art
Information concerning the chemical composition of blood is widely used to assess the health characteristics of both people and animals. For example, analysis of the glucose content of blood provides an indication of the current status of metabolism. Blood analysis, by the detection of above or below normal levels of various substances, also provides a direct indication of the presence of certain types of diseases and dysfunctions.
Persons that have diabetes have a common characteristic in that their bodies have difficulty maintaining reasonable blood glucose levels during various times of the day. In order to allow for survival and avoid long-term complications, most persons with diabetes take medication in an attempt to keep their blood glucose at a reasonably constant level.
The variation in blood glucose levels is a function of many different parameters, such as eating habits, medication, stress, exercise level, etc. The two most common causes of variations in blood glucose levels in persons with diabetes are meals and diabetes medication.
Several methods exist for measuring blood glucose levels. One method is to obtain a blood sample from the patient. The blood sample is placed on a chemically treated carrier and is inserted into an instrument. The instrument analyzes the blood sample and provides a blood glucose level reading in a short period of time. However, the blood sample method has drawbacks, including the painful and invasive nature of the test, which provides an avenue for infection.
An alternative measurement method is the near-infrared quantitative analysis instrument which non-invasively measures blood analytes. Non-invasive quantitative measurement instruments are generally known. See U.S. Pat. Nos. 5,086,229; 5,028,787; 5,077,476; 5,218,207; and 5,703,364. Non-invasive measurement is ideal for persons who must regularly monitor their blood glucose. The non-invasive blood glucose measurement instrument analyzes near-infrared energy following interactance with venous or arterial blood, or transmission through a blood-containing body part. These instruments give accurate blood glucose level readings and readily lend themselves to at-home testing by diabetics. Typically, the measurement is performed on a finger of the subject.
A limitation of the near-infrared blood glucose measurement instruments has been that near-infrared quantitative measurement instruments must be highly precise in their measurement capabilities. Since the amount of glucose in the body is less than one thousandth of the total constituents, variations of the constituents which exist among different people has in the past made highly precise instruments necessary in order to obtain an accurate measurement.
In addition to the near-infrared technology, there are other technologies that have promise for measurement of blood glucose, such as radio-frequency technology. Such devices are less expensive than near-infrared quantitative measurement devices, however, radio-frequency measurement devices do not provide reasonable precision and are therefore lacking.
Thus, there is a need for accurate non-invasive measurement of blood analytes when using technology that does not provide precise direct measurement.